The present invention pertains to steels containing a significant amount of metastable austenite (5%-100%). Austenite is deemed metastable if it transforms to martensite upon mechanical deformation. Such martensite is called deformation-induced martensite, which is stable until the steel is heated to high temperatures upon which the martensite reverts to austenite.
Due to the high work hardening rates associated with the deformation-induced transformation of metastable austenite to martensite, steels containing metastable austenite are sometimes rolled at ambient—or greater—temperatures to achieve high yield and tensile strengths.
If such a steel, in a rolled condition, was to be coated for protection against corrosion, then the high strength of the rolled steel introduces unique challenges during the coating process because coating lines have typically been designed for lower strength steel products. The increased strength causes challenges related to the ability to pull the strip through the line, the ability to bend the strip around rolls, and the ability to perform any shape correction by way of tension leveling or other means.
Furthermore, in some coating techniques, the steel strip is subjected to high temperatures, which result in some or all of the deformation-induced martensite reverting back to austenite. As a result of this reversion, the mechanical properties of the steel strip would degrade, thereby losing the beneficial effects of the earlier rolling process.